The preparation of oriented layers of crystallographically materials is critical in a number of technical areas. For example, high temperature superconductors often employ epitaxially oriented layers of, e.g., YBCO to achieve desired properties. Similarly, epitaxially oriented films such as conductive oxides, ferroelectric, ferromagnetic, piezoelectric, insulating, and semiconductive materials are desired in the areas of microelectric and opto-electric devices. To achieve the desired crystallographic orientation, e.g., epitaxial orientation, of materials such as YBCO, SrRuO3, PZT, Ba1−xSrxTiO3, La0.7Sr0.3MnO3, and Si, extensive work has focused on the underlying structure or substrate onto which the oriented layers are deposited.
Stronium ruthenate (SrRuO3 or SRO) is a conductive metal oxide material and it has been used as an electrode in ferroelectric capacitor applications. Epitaxial SrRuO3 thin films have been previously deposited upon stronium titanate (SrTiO3 or STO) substrates (see, Chen et al., “Epitaxial SrRuO3 thin films on (001) SrTiO3,” Appl. Phys. Lett., 71 1047 (1997). Strontium titanate is a dielectric oxide and has been previously described as a suitable base substrate, e.g., in U.S. Pat. No. 6,541,136. Stronium titanate has also been previously described as a buffer material in superconductive structures, e.g., in U.S. Pat. No. 6,562,761 wherein strontium titanate is suggested as a buffer layer on selected metal substrates and selected single crystal substrates, and in other microelectronic structures, e.g., in U.S. Pat. No. 5,471,364 wherein strontium titanate is suggested as a buffer layer having a moderate dielectric constant.
Despite the many prior uses of both stronium ruthenate and stronium titanate, the use of stronium titanate alone or the use of a mixture of stronium ruthenate and stronium titanate as a buffer layer has not been previously described upon an IBAD-magnesium oxide layer in a coated conductor superconducting structure. Additionally, the use of a mixture of stronium ruthenate and stronium titanate as a buffer layer has not been previously described as a layer in other electronic applications such as ferroelectric, ferromagnetic, piezoelectric and the like.
It is an object of the present invention to provide composite structures including a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate (SrTixRu1−xO3 where 0<x≦1) directly on a magnesium oxide interlayer where the buffer layer is suitable for subsequent growth of a thin film layer, e.g., a superconducting layer, thereon.
It is another object of the present invention to provide composite structures including a buffer layer of a mixture of strontium titanate and strontium ruthenate (SrTixRu1−xO3 where 0<x<1) where the buffer layer is suitable for subsequent growth of a thin film layer thereon.